A broad based program to characterize the normal and activated monocytes and macrophages of animals and man in terms of structure and function. Emphasis will be placed on the biology and chemistry of the plasma membrane and the processes of pinocytosis, phagocytosis and fusions within the vacuolar apparatus. The composition, turnover and flow of the plasmalemma and endocytic vacuole membrane will be followed by surface radioiodination, endogenous labelling and ultrastructural analysis. The fate of plasma membrane enzymes will be established. Procedures are outlined for defining the antigenic moieties on the macrophage surface and the characterization of the Fc and complement receptors. The role of fatty acyl groups of membrane phospholipids in modulating endocytosis will be studied. The mechanisms of macrophage cytotoxicity will be examined. The intracellular parasitism of T. cruzi and macrophage populations is under study. Methods for the isolation and cultivation of human monocytes will be perfected and the cell characterized in long term culture.